The present invention relates to an improved method of preparing a telogen of the structure CF.sub.3 CFClI The method involves reacting a mixture comprising iodine, iodine pentafluoride, and chlorotrifluoroethylene (CTFE) in the presence of an aluminum bromide catalyst for a time sufficient to form the telogen. The resultant telogen is advantageous for telomerizing fluorinated olefins.
Chambers et al. in J. Chem. Soc., 3779 (1961), teach the reaction of iodine with iodine pentafluoride to form iodine monofluoride. This reference also teaches that the iodine monofluoride can react with fluorinated olefins such as CTFE at room temperature without catalysts to form moderate yields (37%) of CF.sub.3 CFClI.
Hauptschein et al. in J. Amer. Chem Soc. 83 (1961) 2383, teach a catalyzed reaction of iodine and iodine pentafluoride with CTFE to form CF.sub.3 CFClI. The method described in this reference comprises a two step process in which iodine and iodine pentafluoride in a molar ratio of at least 2:1 were reacted in the presence of an aluminum metal/aluminum iodide catalyst at a temperature of 100.degree.-175.degree. C. to form iodine monofluoride. The iodine monofluoride was then reacted with CTFE in a second step at room temperature to form less than a 50% yield of the desired telogen.
The inventors herein have now discovered that by using the simple process and reactants of the present invention they can obtain good yields of CF.sub.3 CFClI.